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Early life stress can disrupt development and negatively impact long-term health trajectories. Reconstructing histories of early life exposure to external stressors is hampered by the absence of retrospective time-specific biomarkers. Defects in tooth enamel have been used to reconstruct stress but the methods used are subjective and do not identify the specific biological systems impacted by external stressors. Here we show that external physical and social stressors impart biochemical signatures in primate teeth that can be retrieved to objectively reconstruct the timing of early life developmental disruptions. Using teeth from captive macaques, we uncovered elemental imprints specific to disruptions of skeletal growth, including major disruptions in body weight trajectory and moderate to severe illnesses. Discrete increases in heat shock protein-70 expression in dentine coincided with elemental signatures, confirming that elemental signals were associated with activation of stress-related pathways. To overcome limitations of conventional light-microscopic analysis, we used high resolution Raman microspectral imaging to identify structural and compositional alterations in enamel and dentine that coincided with elemental signatures and with detailed medical and behavioural data. Integrating these objective biochemical markers with temporal mapping of teeth enables the retrospective study of early life developmental disruptions and their ensuing health sequelae.

Early-life dietary transitions reflect fundamental aspects of primate evolution and are important determinants of health in contemporary human populations. Weaning is critical to developmental and reproductive rates; early weaning can have detrimental health effects but enables shorter inter-birth intervals, which influences population growth. Uncovering early-life dietary history in fossils is hampered by the absence of prospectively validated biomarkers that are not modified during fossilization. Here we show that large dietary shifts in early life manifest as compositional variations in dental tissues. Teeth from human children and captive macaques, with prospectively recorded diet histories, demonstrate that barium (Ba) distributions accurately reflect dietary transitions from the introduction of mother's milk through the weaning process. We also document dietary transitions in a Middle Palaeolithic juvenile Neanderthal, which shows a pattern of exclusive breastfeeding for seven months, followed by seven months of supplementation. After this point, Ba levels in enamel returned to baseline prenatal levels, indicating an abrupt cessation of breastfeeding at 1.2 years of age. Integration of Ba spatial distributions and histological mapping of tooth formation enables novel studies of the evolution of human life history, dietary ontogeny in wild primates, and human health investigations through accurate reconstructions of breastfeeding history.